Key controlled numerical digit register equipped with discharge tube means



Aprll 27, 1948. G. DEAKIN 2,440,249

KEY. CONTROLLED NUMERICAL DIGIT REGISTER EQUIPPED WITH DISCHARGE TUBEMEANS Filed April 21. 1944 4 Sheets-Sheet 1 April 27, 1948. G. Dr-:AKIN

KEY CONTROLLED NUMERICAL DIGIT REGISTER EQUIPPED WITH DISCHARGE TUBEMEANS Filed April 21, 1944 4 Sheets-Sheet 2 AGENT April 27', I1941s.

G. DEAKIN v .KEY CONTROLLED NUMERIGAIJ DIGIT REGISTER EQUIPPED wITH.DISCHARGE TUBE MEANS Filed April 21,

4 Sheets-Sheet 5 AGENT G. DEAKIN KEY CONTROLLED NUMERICAL DIGIT REGISTERApril. 27, 194s. 2,440,249

EQUIPPED WITH DISCHARGE TUBE MEANS y 4 Sheets-Sheet 4 Filed April 2l,1944 AGENT Sk ES E MSR atented` pr. 27, M

KEY CONTROLLED NUMERICAL DIGIT REG- ISTER EQUIPPED WITH DISCHARGE TUBE:MEANS Gerald Deakin, New York, N. Y., assignor to InternationalStandard Electric Corporation, New York, N. Y., a corporation ofDelaware Application April 21, 1944, Serial No. 532,142

25 Claims. l

This invention relates to new and usefulimprovements in switchingsystems of the type useful in controlling telecommunication.

The object of the invention is to provide `a simple key-set controllerselectively switching in circuit a relatively small number ofresistances for controlling as many different switching operations asthere are keys, For instance, a ten-button key set is provided with veresistances for controlling the performance of a desired one of tenswitching operations.

In accordance with the present invention, a responsive or registeringdevice is interposed between the key set and the switching device. Itcomprises electric discharge devices arranged in aY number of groupsless than the number of keys.

In the preferred embodiment here disclosed six identical vacuum tubecircuits have their grids connected in multiple to one wire of atwo-wire line connected with the key set. When the register is idle, thecommon lead is connected to ground through, e. g. a resistor of, e. g.5,000 ohms. When the register is picked up, which in an automatictelephone system means that the line is closed to ground at the centraloffice through the subscribers set, the free end of a resistor of,e. g.1,000 ohms also attached to this common lead is connected to a commonbattery of 48 volts. It will be assumed, for the purpose of determiningthe specific resistances and potentials used, that the maximum totalloop resistance of a subscribers line will not exceed 500 ohms and thatthe leakage resistance from the one line wire to ground or from the oneline wire to the other will not be less than 25,000 ohms. Otherresistance values could be used, but an insulation resistance of notless than 25,000 ohms is easily realized in any modern cable plant.

In operation, the potential of the common lead depends upon the value ofthe combined series line and key controlled resistance to ground inmultiple with any leakage. An ample series of potentials may be obtainedto operate any one of six tube circuits in multiple with theaforementioned leakage. The operation of one, two or three of these tubecircuits makes it possible to select any one of ten digits, to changeover from one selection to the other, or to eiect a premature releaseshould the calling subscriber hang up before the register isdisconnected in the normal way after completing selection of the calledline. The use of tube circuits in this manner eliminates timed circuits,timed relays or step-by-step means 2 now so generally used indial-controlled register circuits. K

In the drawings:

Figs. 1 is a diagram of a telephone substation circuit equipped with akey set;

Fig. 2 is explanatory of the order in which the key contacts areoperated;

Figs. 3-8 show the mechanical arrangement of the key set, Fig. 3 being asection along 3-3 of Fig. 5, Fig. 4 a section along 4--4 of Fig. 6, Fig.5 a section along 5 5 of Fig. 3, Fig. 6 a section along 6 6 of Fig. 5,Fig. 7 an end view of the key set with part of the wall broken away, andFig. 8 is explanatory of the manner in which the contacts are operated;c

Fig. 9 illustrates a telephone set equipped with a key controller;

Fig. 10 is a diagram oi' the register circuit;

Fig., 11 is explanatory of the functioning of the control circuit; and

Fig. l12 is a tabulation of the resistance values used and potentialsapplied to the register.

subscribers set circuit (Figs. 1, 2 and 9) When the subscriber removesthe handset from the swltchhook, the ringer is disconnected and the aand b wires of the line circuit are connected through the usual`induction coil, transmitter and switch-hook contacts. The ringer isdisconnected so that the condenser shall not receive an appreciablecharge between the keying of digits and thus produce unwantedpotentials.

The mechanical details of the subscribers keys will be disclosed belowin connection with Figs. 3-8 after their electrical functions have beenexplained in connection with Figs. 1 and 2.

When any key l-O is depressed, contact l of the home contact nest closesand short-circuits the induction coil and transmitter. Immediately afterthat, contact 2 opens and removes a shortcircuit around resistor RX andthe iive keying contacts CI to C5. Resistor RX is adjusted individuallyat each station so as to make the combined series resistance of RX plusthe line wire LR in the loo`p to the central oilice 500 ohms i-5%. Tofacilitate adjustment at the sub-station, it is proposed to use aplug-in radio type resistor for RX,

The above-mentioned operations take place immediately upon thedepression of any key. When any one of keys l to 4 is about M1depressed, one of the contacts CI to C4 is momentarily opened by the keyin passing, thereby momentarily introducing a resistor RI R2, R3 or R4,as the case may be, into the line circuit. Each resistor Rl to when itis released, it restores 'instantly'to its n'lor-Y mal position underthe tension'of al spring with'- out switching in any of the resistancesRI to R5. The keys 'may be depressed very rapidly or Svery slowly; thespeed of their operation is without effect on the responsive means.

When any one of the keys to 0 is depressed, three contacts aremomentarilyopened.4 instead of two, the i-lrst when the key is 1Adepressed,.the second when the key is 1A; way down, and the third whenthe key is.% depressed.

'Ihe contacts which' each key momentarily opens when it is depressed areindicated by'the letters CI, C5, etc. placed immediately below the keybutton on the key contactfdiagram (Fig,l 2). The contacts are listedtopV downin th .order in which they are opened.V It `will befseen thatcontact C5 is alwaysfthellas'tto open. It introduces resistor R5 intothe line lcircuit which operates the change-over tube circuit in theregister. A

Should the subscriber hang .up before .com pleting keying, the linecircuitwillbe openedland the shunt will be removed from the "5,000 ohmresistor R1 in the register circuit. (Fig. `10) .theremeans, such asshown in Figs. 5 and 6, is a sliding plate I3 which engages the 4homecontact nest Il and is normally kept in the position shown by thetension of the spring nest. When amr key is depressed, the slanting partI4 of the plunger I (Fig. 5) forces the sliding plate I3 to the left,thereby operating the home contact nest.

The arrangement of the pins in sliding bars BI to B5 (see Fig. 8) agreeswith the diagram (Fig, .10.

2). YFor example, rwhen key 6 is depressed and released, theiollowingoperations take place in the" order Vlisted t a. Sliding plate I3operates home contact nest b...When the key is about 1A Way down, wiper6 engages -pin-PI 'and forces bar BI to the right, thereby openingvcontact CI. Almost immediately thereafter, part 6 releases the pin andbar 4BI is forced back sufficiently byV contact CI to by permitting thepotential ofthe common lead to increase toa maximum and operate.therelease tube circuitNo. 6. v

Key set assembly (Figs, 358) One form of a ten-button key set is shownin these figures. It comprises ten keyY plungers I of which arectangular portion pierces a housing 2 and is free to slide in saidhousing. The plunger is slipped through .the housing from the bottom,after which button :i is attachedto it in any suitable manner. Thelower' part 'fof .the plunger I is round and over this partis slippedretractile spring 4, which rests against thejbottfom plate 5 of thehousing and againstthe rectangular part of the plungerat' the'. top.vV',Ihuslthe spring normally keeps the plunger'in the position shown. Aslanting wiper 6 projectsirom Y.each plunger.

When any key is depressed, it longitudinally displaces Atwoor three offive horizontallbars, BI, B2, B3, B4, and B5 in accordance' .with thesetting of pins, PI, P2, P3, P4, ete., whichproject -from the barsinpatterns that determine the sequence of contacts CI-C5 Vthat will beoperated by the key. Each of the iive bars engages atone end a contactCI toC5 (see particularly Figs, 6 and 7). Part 'I is welded tobars BIvand`B5 and operates the twoouter contacts CI `and C5 when either bar ismoved by a key. Part 8 projects from'BZ and B4 and operates contacts C2and CII. Barl.B3 operates contact C3 direct. The other ends of the vebars rests against an insulated piece 9 attached to band spring!) (seeFigl'); Spring 9 keeps all the five bars in engagementwith theircorresponding C contacts. Movement of the spring` 9 is limited by backstop I2. The ve bars are heldin position by slotted insulator ,supportsIIJ (Fig. 5) which are attached to the bottoni of thehousingt.

' Supported from the housing by any suitable allow its closure.

c.,When .the key is about le waydown, bar..BS is similarly/'forced 'tothe, right.throughJP,Y and momentarilyopens contact C3.`

d. When the key is about.% way down, bar.B5 is kforced, lto theright byP5 andcontact C5 .is

momentarily opened.

e. When the key is all the way down, bar B5 is released and contactC5re-closes.

',f. When pressure is removed. from. the `key button, the plunger isquickly lrestored tofnormal by retractile spring 4. Wiper 6, however,.engages the three pins in question fromtheunder side, thereby forcingthem to .the ,left against common back stop 9. Contacts CI, C3 V and C5are thus not opened on the returnstroke. As .Wiper-.,wpasses eac-h pin,spring!!,restoresv thebar to normal.

When the `plunger is fully restoredtoits normal position, sliding plateI 3 Vresumes its 'the second. This is particularlyl truen the ease ofkey o which operates baises, B2i and 135.

Slubscrzfbers set assembly (Fig.9)

One form of table set l25 equipped with handset 20 and key set 2| isshown in'IEig '9. fI get the keys out of the way when removing andreplacing thehandset, and to obtainthe required depth for the key setwithout disturbing thenorial arrangement of ringer, induction coilvand.v ,con-

.denser attached to the base, the keys are backof the handset. -The keysare guarded against accidental operation or damage by 'sidea'rid `Vrearwalls 22 and 23. v

Thedepression 24 in -frontof .the .key set..2l and the outward slope ofthe Wel/1123 atjithe rear vof lthe keys afford a meansof pickingupthetable s et without disturbing thehandset.'

Operation of the register'vial) For the details of the register circuit,selectors,

lline finders and associated devices attention is directed tomyVcopending application Serial No. 521,160, `iiled February 5,'1944'.'1-Ier'e only 'so muchY isrshown `as is necessary forillustrating automatic means lfor variably lresponding to the actuationofthe key set, for registering the response vand transmitting it toselectors or the like used. e. g. in the establishment oraconnectionVbetween calling and called subscribers -When the subscriber removes thehandset 20,

an idle register (Fig. ,10) vand a iirst linender Whena Y digit keyed bythe subscriber has been recorded, the a Wirecof the selector-circuitisgrounded are connected with the callingline.

and apotential is placed o n the bf wireso that theselection ofthealledline caribe-made. AIn

.the present casegXR relays are substituted for the digit switches oirnyapplication SerialNo. 521,-

160, filed February 5, 1944, ,in the same VIrl-'inner as in my copendingapplication SeriallSIo.` 527,921,

led March 24, 1944, now Patent No. 2,433,345, dated Dec. 30. 19,47-

When relay BAR releases, -it opens thecircuit of slowreleasingrelayLDLR, thereby-momentarily grounding both sides 0f the .calling lineforth@` purpose of discharging Ythe Yenergy stored in the line.AWhen-LBR makes its back contact, the V2 20 grids of thestlx triadecircuits are connected to the b wire. ;R13R,operat es HTR. lI-ITRoonnectsresistor R1, also attached to the b` Wire,

to theexchangel v olt battery. 'I'he `secondary winding ofthedialingtone-transformer TT is 2 5 bridged across the calling line andthe primary circuit is closed over a front contact of RBR. If required,filter F may be placed inthe common valve leadtoprevent false operationof the valve circuits due to possible undesirable potentials 30generated by theqdialing tone circuit. ap-

plies high tension battery to the valve circuits.

, RBRalso vOperates RIR which Controls release and the vdischarge tubemeansmarked Tube Ct.

#6 in Fig. 10 contrOlsthe release as will be here- -inafter explained invgreater detail. ating .potential for which leach pairof triodes is setis shown in Figs. 11 Vand 12. When the potentials applied-to the gridsof a pair of trlodes bear a predettir11 linedV relationship Ato oneanother, i. ve. when they are Vthe same, then the associated gasvalveGVv strikesy andoperates its GVR relay.

Whenthe connectionis lestablished with the register, the subscribers setis bridged acrossthe line and the subscriber hears the --dialing tone.

vThe resistance of theloop circuit, as previously `stated, is A500 ohmsorflessand the potential on a common lead (point E-I,"Figs. 10 and 11)is Well below the Operatinglimit of any ofthe Valve circuits. -l

When the subscriberY depresses a key for the .iirst.digit, his inductioncoil `and transmitter are Ashort-circuited and RX (Fig. 1) is cut into-the line circuit. 'The potential of point-E-l is now 12.7 volts (Fig.12). This is the non-release con- 7 dition during keying. If key 1 isdepressed, then the next stepis the insertion of resistor Rl, which:increases the loop. resistance to 3500 ohms and thepotential of thecommon tube lead to approximately `32..volts, .whereupon the No. lpairof .17

The 45 ,dischargetube means marked Tube Ct. #5 controls the change-overfrom one, digit to the next,

The Voper- 50 .triodesfy the. grid offone of which is permanentlyconnectedto this and only this potential, operates and restheassociatedgas valve, all inthe well-known manner. GVRI operates. When zikey 1 isnearly fully depressed, it momentarily cuts in R5 (Fig. 1) vand appliespotential of approximately 18 volts, whereupon the No. 5 pair Aoftriodesoperates and energizes GVRS (Fig. 10).

GVR5 grounds the armature of relay GVRI, thereby causing XRI to operate.GVRS also operates DTR which looks up over a front contact of RI R anddisconnects the dialing tone. Shortly after GVR5 makes its irontcontact, itv opens its back contact and releases HTR. HTR falls oii,de-ionizes GV and releases GVR of tube circuitsNos. 1 and 5. When groundis removed from the winding of XR, the latter locks up over a frontcontact in series with the Winding of TRI andaront contact of RCR. TRIoperates, and transfers the tube circuits to the second set -of XRrelays over back contacts of TR2.

The second and following digits are, keyed in lthe; same manner as theiirst, tube circuits Nos. 1 to 4 or combinationsof them being operatedaccording to the key depressed as indicated in the -following table. Thetube circuit No. 5 is always the last tobe operated. It locks up theproper XR relay or relays and prepares immediately for thenextselection.

GVR and PN-Poten- Key Depressed XR Relay tial Con- Operated nected lPN-l 2 2 3 3 4 4 l+2 A 5 1+3 6 1+i 7 2-1-3 8 2-1-,4 9 Sel-4 10 I l.Asexplained in my copending applications, in multi-potentialcontrolsystems like the one here disclosed, the selectors are startedbythe register Aand hunt for a potential corresponding to the oneconnected in the' register. When the selector nds the desired potentialits driving circuit is --opened by the firing of the gas valve in theregister.

Ordinarily the registeris released upon the completion of selection.However, should Vthe subscriber hang up before selection is complete,.the line circuit is opened and the potential of point E-l is increasedto the'maximum as indicated in Fig. 12, applying 40 volts to the gridsand operating tube circuit No. 6. GVRS opens the circuit ofthe releaserelay RIR which restores the circuit to normal.

What is claimed is:

1.111 a telecommunication system, a plurality of lines, each having amulti-digit number, means including a plurality of stages .of numericalselector switches for establishing a, connection between a calling and acalled line, a plurality of keys for each line, a normally inactiveregister comprising digit switching means for Variably operating theselectors in accordance with the different digits of the called number,said register comprising a plurality of electric discharge tube meansless innumber than the keys associated with a line, means forestablishing a conductive connection from the keys to the tube` means, asource of direct current potential, means con- 5 .,trolledlby. the keysover the connection for selectively operating the tube means from saidsource, and means controlled by thev tubes for variably controlling thedigit switching means.

2. The system according to claim l', and in which the register comprisesa digit Vswitchv .for each digit, means controlled by .the tube meansfor operating all the digit switches, and means controlled by one of thetube means for successively connecting the other tube means from onedigit switch to the next.

3. 'Ihe system according to claim l, and in which one of the tube meansoperates upon each actuation of any key, and means controlled by thelast-mentioned tube means for preparing the register for the next digit.

4. The system according to claim 1, and in which each line is providedwith ten keys and the register four discharge tube means, meanscontrolled by four keys for selectively operating the four tube means,and means controlled by each of the other six keys for operatingtwo ofsai-d tube means in six diierent combinations.

5. The system according to claim l .,-and'fin which each line isprovided with ten keyseiand the register with four dischargetubemeans,means controlled by four keys for selectivelyV operating thefour tube means, means controlled by each of the other six keys foroperating two of said tube means in six different combinations, and afifth tube means in the register operable upon the actuation of any key,and means controlled by the iifth tube means for associating the fourtube means with the digit switching means.

6. The system according to claim l, and release means for the registercontrolled by one of the tube means. Y Y

7. The system according to claim 1, a plurality of resistances for eachline, contacts controlled by the keys for selectively connecting saidresistances in the connection for selectively operating said tube means.

8. The system according to claim 1, and a control grid for each tubemeans connected in multiple with said connection.

9. The system according to claim 1, and in which each tube meanscomprises a pair of tubes.

10. The system according to claim 9, and in which each tube is `atriode, a multiple connection from the grids of one triode of each pairto said connection, and connections for applying different potentials tothe'grids of the other trio'des of each pair.

11. In a switching system, a source of D. C. potential, a switchvariably operable depending on the potential applied thereto, aplurality of two-wire lines, means for connecting a line with the sourceand the switch, keys associated with each line, home and keying contactscontrolled by l said keys, at least four different resistances connectedin series with one another between the line wires over home contacts, ashunt normally closed V.around each resistance by. a different keyingcontact, means for actuating the home contacts when any key is operated,and means controlled by each key for successively momentarily openingdiierent keying contacts.

l2. In a switching system, a source of D. C. potential, a switchvariably operable depending on the potential applied thereto, aplurality of two-wire lines', means for connecting a line with thesource and the switch, keys associated with each line, home and keyingcontacts controlled by said keys,'ve different resistances connected inseries with one another between one line wire and a normally open homecontact, the later connected with the'other wire,'a shunt normallyclosed around each resistance by a dlierent keyingcontact, a sixthresistance for each line in series with the five resistances of a valueapproximately equal to the diierence between the loop resistance of theline and a predetermined value, a shunt around the six resistancesincluding a normally closed home Contact, means for actuating the homecontacts when any key is operated, and means controlled by thekeys forsuccessivelyv momentarily opening different keying contacts.

13. In a switching system, a source of D. C. potential, a switchvariably operable depending on the potential applied thereto, aplurality of two-Wire control circuits, means for connecting one of thecircuits with the source and the switch, ten keys associated with eachline, a pair of normally closed keying contacts for each key, normallyopen and normally closed home contacts, ve different resistances foreach line connected in series with one another between one line wire anda normally open home contact, the latter connected with the other wire,a shunt normally closed around each resistance by a diiierentkeying-contact, a sixth Vresistance for each line in sei'es with theiive resistances and having a value approximately equal to thedifference between the loop resistance of the line and a predeterminedvalue, a shunt around the sixth resistance and the keying contactsincluding a normally closed home contact, means for actuating the homecontacts when any key is operated, a longitudinally movable plunger foreach key, and means controlled by each plunger for successivelymomentarily opening predetermined keying contactsv during its movementin one direction.

14. In a telecommunication system, a plurality oi lines each having amulti-digit number, means including a plurality of stages of numericalswitches for establishing a connection between a calling and a calledline, a register for successively controlling the operation of saidswitches, a controller comprising ten keys associated with each line,each key adapted to variably operate the register in accordance with thedifferent digits of the called number, a plurality of but less than tendischarge devices in the register ccnnected to a common lead, keyresistances, contacts Vcontrolled by the keys for connecting the keyresistances in series with the line, the potential of the common leaddepending upon the value of the combined line and key resistances inseries to which said devices are responsive, a relay associated witheach device and controlled by them, and a selector control circuitcontrolled by said relays in accordance with successive digits of thecalled number.

15.4The system according to claim 14, and in which one of said relayscontrols the change-over of the register control from one selector tothe next.

16. The system according to claim 14, and in which one of said relayscontrols the release of the register.

17. In lan automatic telephone exchange system, a plurality ofsubscribers two-wire lines each having a multi-digit number, meansincluding a plurality of stages of numerical selector switches forestablishing a connection between a calling and a called line, aplurality of registers for successively controlling the oper-ation ofsaid switches, ten keys associated with each line for Vvariablyoperating a register in accordance with the different digits of thecalled number, means for connecting a calling line with an idleregister, six pairs of triodes in each register, one triode in each pairhaving its grid connected in multiple to a common lead to one of thewires of the calling line, a first connection to ground from the commonlead over a resistance closed while the register is idle, a secondconnection from said common lead to battery over a resistance, keyresistances, contacts controlled by the keys for connecting the keyresistances in series with the line, the potential of the common leaddepending upon the value of the combined line and key resistances inseries to ground and in multiple with leakage resistance, a different D.C. potential connected to the grid of the second triode of each pair, apair of triodes being adjusted to operate when the potentials applied tothe grids of the triodesbear a predetermined relationship to oneanother, a relay associated with each pair of triodes and controlled 4bythem, and a selector control circuit controlled by said relays.

18. In an automatic telephone exchange system, a plurality ofsubscribers two-wire lines each having a multi-digit number, the loopand leakage resistances of a line having predetermined values, meansincluding a plurality of stages of numerical selector switches forestablishing a connection between a calling and a, called line, aplurality of registers for successively controlling the operation ofsaid switches, ten keys associated with cach line for variably operatinga register in accordance with the different digits of the called number,means for connecting a calling line with an idle register, six pairs oftriodes in each register, one triode in each pair having its gridconnected in multiple to a common lead to one of the wires of thecalling line, a first connection to ground from the common lead over arelatively high resistance closed while the register is idle, a secondconnection from said common lea-d to battery over a relatively lowresistance, key resistances, contacts controlled by the keys forconnecting the key resistances in series with the line, the potential ofthe common lead depending upon the value of the combined line and keyresistances in series to ground and in multiple with leakage resistance,a .different D. C.

potential connected to the grid of the second triode of each pair, apair of triodes being adjusted to operate when the samepotentials areapplied to the grids of both triodes, a relay associated with each pairof triodes and controlled by them, and a selector control circuitcontrolled by said relays.

19. In an automatic telephone exchange system, a plurality ofsubscribers two-wire lines each having a multi-digit number, the loopresistance of a line being less than about 500 ohms and the leakageresistance less than 25,000 ohms, means including a plurality of stagesof numerical selector switches for establishing a, connection between a'calling and a called line, a plurality of registers for successivelycontrolling the operation of said switches, ten keys associated witheach line for variably operating a register in accordance with thedifferent digits of the called number, means for connecting a callingline with an idle register, six pairs of triodes in is idle, a secondconnection from said common lead to a 48 volt battery over a 1,000 ohmresistance, key resistances, contacts controlled by the keys forconnecting the key resistances in series with the line, the potential ofthe common lead depending upon the value of the combined line and keyresistances in series to ground and in multiple with the leakageresistance, a different D. C. potential connected to the grid of thcsecond triode of each pair, a pair of triodes being adjusted to operatewhen the same potentials are applied to the grids of both triodes, arelay associated with each pair of triodes and controlled by them, and aselector control circuit controlled by said relays.

20. In an automatic telephone exchange system,` a plurality ofsubscribers two-wire lines each having a multi-digit number, meansincluding a plurality of stages of numerical selector switches forestablishing a connection between a calling and a called line, aplurality of registers for successively controlling the operation ofsaid switches, ten keys associated with each line for variably operatinga register in accordance with the different digits of the called number,means for connecting a calling line with an idle register, six pairs oftriodes in each register, one triode in each pair having its gridconnected in multiple to a common lead to one of the wires of thecalling line, a iirst connection to ground from the common lead over aresistance closed while the register is idle, a second connection fromsaid common lead to battery over a resistance, key resistances, contactscontrolled by the keys for connecting the key resistances in series withthe line, the potential of the common lead depending upon the value ofthe combined line and key resistances in series to ground and inVmultiple with leakage resistance, a different D. C.

potential connected to the grid of the second triode of each pair, apair of triodes being adjusted to operate when the same potentials areapplied to the grids of both triodes, a relay associated with each pairof triodes and controlled by them, a selector control circuit controlledby four of said relays.

21. The system according to claim 20, and in which one of said relayscontrols the change over to the next.

22'. The system according to claim 20, and in which one of said relayscontrols the release of the register.

23. In an automatic telephone exchange system, a plurality of telephonesubstations, switch- Vidual contacts controlled by each of the keys eachregister, one triode in each pair having its and a common contactcontrolled by all the keys, a device selectively operable` under thecontrol of the key contacts over said circuit, a ringer and a condenserin series in the circuit at each station, and means oper-able while anykey is operated for disconnecting the ringer and condenser from thecircuit.

24. In an automatic telephone exchange system, a plurality of telephonesubstations, switching devices for connecting a calling with a calledstation, a circuit leading from each station towards the switchingdevices, a source of D. C. Potential in said circuit, a plurality ofresistances at each station connected in the circuit, a'set of keys,contacts short-circuiting the resistances controlled by the keys, aringer, a condenser and circuit at eachstation, 4said' home Vcontactshort-v circuiting allthe keys, andmeansl responsive to the actuationof-vany' key, of opening the home contact and maintaining it 'open'whilethekey is operated;

Y 25.`In. an automatic telephonenexchangesys'' tem, a source ofl D. C.,vpotential, a plurality of telephone substations,switching'devicesforfcontrolling V,the connectingof a calling with acalled station, a, two-wire circuit-leading :from eachstation-towardsthe switchingdevices, means for connecting the Vsourcewith 'the' callingiline, five resistances at each station connected 1nseries in the circuit, ten keys at each station; contacts. controlled`Joy; saidA keys. Yshort.;clrcuitimg the .resistapnces,` meanscontrolled; by 'the .keysrfor sedenser-"fand a Y. normallyV Vclosedf'home icontact in y seriesi'in lthe'cireuit at= each station, said homecontactfshortfcircuitn'g allthe keys'and resistances, and v4:means`responsive' to the f actuation of rany key, fory Vopening the --homecontact and maintaining it f open while'the'key is operated'. GERALDDEAKIN.

REFERENCES CITED Th'efollowing vreferences are of recordinthe' l'e ofvthispatent:

UNI'I'ED STATES'PATENTS Number: Name-.r Date.v

1,337,715 M'cQuarrie" 4A131210; .1920 1,854,106@V Car.penter1 V- Apr.12, 1932 1,982,290 Gardne-rf Nov. 27, 1934 2,269,022 Hech't ,Jan.6,'.1942 2,307,523?` Parkinson-1 Jan: 5; 1943

